Illustrated Glossary of Organic Chemistry
Rate
equation (
rate law
;
rate
expression):
A mathematical description of a
reaction's rate
as a function of the concentration of the
reactants
, and the
rate
constant (k). Usually in a form similar to
rate
= k [
reactant A
] [
reactant B
].
In an
S
N
1 reaction
, the
rate-limiting step
is
ionization
of the carbon-
leaving group
bond
to
produce
a
carbocation
. This is a
unimolecular
process, for which the
rate
equation is:
Rate
= k [
R
3
C-
LG
].
In an
S
N
2 reaction
, the
rate-limiting step
involves formation of the carbon-
nucleophile
bond
simultaneously with
ionization
of the carbon-
leaving group
bond
. This is a
bimolecular
process, for which the
rate
equation is:
Rate
= k [
R
3
C-
LG
] [
Nuc
].
Related terms:
Termolecular
,
trimolecular
,
reaction mechanism
,
equilibrium constant
,
K
eq
,
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